National Repository of Grey Literature 66 records found  previous11 - 20nextend  jump to record: Search took 0.01 seconds. 
Mechanical and fracture mechanical tests of a special type of steel
Gajdoš, Lubomír ; Šperl, Martin ; Šorm, Filip
Research report on testing of mechanical and fracture mechanical properties of special type of the steel. Between the main results of the research belong fracture toughness in the terms of J integral parameters, constants for crack grows rate in the type of steel used to railway bogies.
Dynamic and static tests of the cotton clothes of dummies used to crash car tests
Šperl, Martin ; Gajdoš, Lubomír ; Šorm, Filip ; Vála, Ondřej
Research report on testing the influences different cotton clothes to material interference during car crash test. The tests were performed in some loading modes for the material composition (dummies skin, cotton, seat belt).
Investigation of fundamental mechanical and fracture mechanical properties of high pressure gas pipeline - location L177 (L177/1 and L177/2)
Gajdoš, Lubomír ; Šperl, Martin ; Šorm, Filip ; Bejdl, Jan
Assesment of mechanical and fracture mechanical properties including the analysis of critical crack dimensions for specific gas pressure and pipelines segments. These magnitudes will be used as a reference properties on the subsequent hydrogen effect investigation to the pipeline steel.
Assessment of gas pipeline reliability based on mechanical and fracture tests of pipe segments\nfrom VTL DN 500 (lane no. 41 and 56) and VTL DN 300 (lane no. 152)
Gajdoš, Lubomír ; Šperl, Martin ; Šorm, Filip
Determination of mechanical and fracture mechanical properties include analysis of the critical crack dimensions for specific gas pressure and pipe segment (material).
Methods No. 25/01/UTAM19 for covering of the buried infrastructure components against laid explosives and cumulative bullets
Šperl, Martin ; Gajdoš, Lubomír ; Wolf, Benjamin
The methodology describes specific procedures for covering of the buried infrastructure components. The purpose of these procedures is low cost protection for the buried technologies against dynamic ground threats. Mainly it is laid explosives and cumulative bullets. The basic procedures of this methodology have been implicated into the gas normative regulation TPG 70204 - Revision 2.
Determination of mechanical and fracture mechanical properties for high pressure gas pipelines (line no. 154 and 223 - DN 500, line 113 - DN 200
Gajdoš, Lubomír ; Šperl, Martin
Determination of mechanical and fracture mechanical properties include analysis of the critical crack dimensions for specific gas pressure and pipe segment.
Methodology for measurement of fast projectiles speed decrement during their penetration through various substances using a digital opto-mechanical device
Šperl, Martin ; Gajdoš, Lubomír ; Wolf, Benjamin
This methodology describes the procedures, the equipment and software used for measurement of the speed decrease of flying projectile through different bulk, silicate and solid masses. The advantage and uniqueness of this methodology consists in ability to measure the attenuation characteristics of various materials during the impact by high speed projectile. The methodology is based on a system of thin plates with optic fibers that function as a light-time gate with a defined pitch.
Fracture toughness testing for improving the safety of gas pipeline
Gajdoš, Lubomír ; Šperl, Martin
For standard fracture mechanical tests flat specimens (principally CT or SENB) are required. This brings problems for investigating fracture mechanical properties of thin-walled pipes because it is necessary to straighten the pipe bands [1]. However, this operation causes internal stresses to be induced not only in the semi-product subjected to straightening but also in finished specimens. A question therefore arises to what extent are then the magnitudes of the fracture toughness determined representative for the actual cylindrical wall. To solve this problem fracture mechanics tests were carried out on flat (straightened) CT specimens as well as on curved CT specimens with the natural curvature. The R – curves as well as the resulting parameters of the fracture toughness, obtained for both types of CT specimens, were compared and it was concluded that the fracture toughness of the pipe material determined on straightened CT specimens was practically the same as that obtained on curved CT specimens.
Changes in dislocation substructure of S235JR steel during fatigue loading
Jandová, D. ; Gajdoš, Lubomír ; Šperl, Martin ; Kaiser, J.
Changes in dislocation substructure were studied in normalized and annealed S235JR steel in relation to the number of symmetrical reversed stress cycles with the amplitude σa = 242 MPa and corresponding mean life Nf = 17,950 cycles. The microstructure of the steel consisted of ferrite with a small amount of pearlite. The substructure was observed in as received condition and after application of various relative numbers of cycles n/Nf, these being 0.25, 0.50 and 0.75. An irregular dislocation net occurred in the virgin specimen, however, during cyclic loading the dislocations started to accumulate gradually in slip bands and to form a cell substructure in grains of favourable crystallographic orientations. Total dislocation density, dislocation density in slip bands and inter-band distance were measured using transmission electron microscopy (TEM). The total dislocation density was found to slightly decrease and the density in slip bands to increase with increasing number of cycles. The results concerning the dislocation density were compared with changes in the microplastic limit (MPL) which were determined by the measurement of the inductance of the “specimen - coil” system. They consisted in a rapid initial decrease at the first stage of the fatigue process and in a gradual increase during the major part of the life. These changes can be interpreted on the basis of changes in dislocation density as was verified independently by X-ray diffraction and nanoindentation tests. On the basis of the measurement of dislocation density by TEM it appears that changes in MPL can be connected with the dislocation density in slip bands rather than with the total dislocation density.
Micro-plastic limit of low-carbon steel CSN 41 1375 as determined by the measurement of electrical impedance
Gajdoš, Lubomír ; Šperl, Martin ; Kaiser, J. ; Mentl, V.
It is generally accepted that not all cyclic stresses below the fatigue limit are non-damaging. Particularly in spectrum loading, the inclusion of some cyclic stresses below the fatigue limi can reduce the fatigue life of a component. It is believed that the boundary between damaging and non-damaging stresses is the so-called micro-plastic limit (MPL) defined as a macro-stress at which dislocation pile-up stresses begin to obstruct the magnetic domains in rotation to the direction of the tensile stress. This paper shows that MPL can be determined from changes in magnetic permeability during tensile loading. In our work, changes in magnetic permeability were measured indirectly - by measuring changes in electrical impedance (a.c. resistence and induktance). Measurements were performed on normalized low-C steel CSN 411375, and the microplastic limit was determined by evaluating

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4 Gajdoš, Libor
1 Gajdoš, Lukáš
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